Instruments and techniques for disc space preparation

ABSTRACT

A series of instruments ( 30, 80, 120, 210, 510, 550 ) are provided for direct-anterior and oblique-anterior disc space and end plate preparation. The instruments ( 30, 80, 120, 210, 510, 550 ) provide precise guidance for channel formation in the vertebral endplates by guiding rotating and bladed cutting instruments ( 122, 250, 580 ). Instrumentation ( 550 ) for oblique-anterior disc space preparation includes compound angulation to account for the angle of approach to the spine and the angulation between adjacent vertebrae. Methods and techniques for use of the instruments ( 30, 80, 120, 210, 510, 550 ) are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of PCT Patent ApplicationSerial No. PCT/US01/05500, filed Feb. 22, 2001 entitled “Instruments andTechniques for Disc Space Preparation” which was published in Englishunder Article 21(2) and which claims the benefit of United StatesProvisional Patent Application Serial No. 60/184,107 filed Feb. 22, 2000entitled “Instruments and Techniques for Disc Space Preparation”, all ofwhich are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates generally to instruments and techniquesfor preparing a site between two adjacent bony segments to receive animplant therebetween. More specifically, the present invention providesinstruments for vertebral end plate preparation to receive interbodyfusion devices or artificial disc implants. The instruments andtechniques of the present invention have particular application, but arenot limited to, direct anterior or oblique-anterior approaches to thespine.

While implants of various types have been utilized throughout the bodyfor various orthopedic bone applications, the present invention hasparticular application to the field of preparing an intervertebral discspace to receive an interbody fusion device to create bony fusion or aspacer providing artificial disc functions. Such procedures may benecessary where the natural disc has degenerated or slipped resulting inpain and discomfort to a patient. The deterioration or movement of thedisc often results in the two adjacent vertebral bodies coming closertogether. A common treatment is to surgically restore the proper discspace height to thereby alleviate the neurologic impact of the collapseddisc space. Typically, the damaged disc is removed and an alternativesubstance is inserted to maintain the proper height. While artificialdiscs have been developed and will likely continue to be developed thatmay be placed in the effected disc space, present procedures oftenutilize a load bearing structure, either man-made or natural, tomaintain the disc height and promote bony fusion between the adjacentvertebrae. Such techniques for achieving interbody fusion betweenadjacent vertebral bodies is well-known in the art, it will not bedescribed further.

U.S. Pat. No. 5,772,661 to Michelson discloses methods andinstrumentation for surgical correction of human thoracic and lumbarspinal disease from an anterior, lateral aspect of the spine. Thispatent discloses methods, techniques, and instruments for lateralplacement of spinal implants. While the application does recognize thatan approach from a lateral aspect of the spine in an area of lordosismay result in angulation between the end plates adjacent vertebra, thisinvention teaches only restoration of the proper angle between thevertebra. Subsequent preparation of the opening to receive an implant,however, is created by over cutting into the end plates of the adjacentvertebra disposed closest and potentially under preparing the end platesdisposed farther apart. Thus, there is a need for end plate preparationwhich not only maintains lordotic angulation of adjacent vertebra, butalso provides for substantial uniform preparation of the vertebral endplates to receive an implant.

International publication WO 98/04202 published Feb. 5, 1998 disclosesmilling instrumentation and methods for preparing a space betweenadjacent vertebral bodies. This publication discloses utilization of amilling device to control the depth of penetration and field of cut ofcutting instruments adapted to prepare vertebral end plates to receivean implant. However, as with earlier approaches to end platepreparation, this publication fails to teach instruments utilized toprovide precise control over cutting depth, height, and angulation. Suchdrawbacks are particularly acute when it is considered that an obliqueapproach to the anterior spine may be necessary where patient anatomydoes not permit easy direct anterior access to the spine.

Thus, there remains a need for improved instrumentation and techniquesfor disc space preparation. The present application is directed to thoseneeds.

SUMMARY OF THE INVENTION

The present invention provides a variety of instruments for precisionguided disc space preparation. While various approaches to the spine maymake use of the instruments according to the present invention, theinstruments are preferably adapted to a direct-anterior oroblique-anterior approaches to the spine. Additionally, the presentinvention contemplates novel methods for disc space preparationutilizing the guided instrumentation of the present invention.

One aspect of the invention includes a distraction window assemblyprovided with removable distraction flanges adapted to be removablyreceived within the window assembly. In a preferred embodiment, aretaining clip is provided that releasably locks the flanges in positionduring use. In a further preferred aspect, the distraction windowincludes arcuate upper and lower bone engaging surfaces to provideintimate contact with the vertebral bodies.

In yet another aspect of the invention, a guide tube is provided forguiding instruments and implants there through. The guide tube acts toalign the instruments and implants as well as protect surrounding tissuefrom damage during the various steps of a procedure. The guide tubeincludes an external locking mechanism operable to lock the guide tubeto the window assembly from the proximal end of the guide tube.Preferably, the locking mechanism is operable without rotation of theguide tube. The external locking mechanism permits an unobstructedinternal working channel and is operable without addition vesselretraction.

In still a further aspect of the present invention, a burr template isprovided for mating engagement with the window assembly. The burrtemplate may preferably include a guide housing having a cutting slot, alinkage assembly connected to the housing and a guide tube connected tothe linkage. The guide tube is controlled to move laterally along thecutting slot while maintaining alignment of the cutting piece in thehorizontal and vertical directions. Still more preferably, the guidetube is maintained at an oblique angle with respect to the housing.Additionally, the burr template may provide the capability ofcontrolling the height of the burr cut into the vertebral body endplate. The burr template assembly includes an incremental adjustmentmechanism adapted to provide defined incremental adjustments of theheight or depth of burr cutting into the end plate for precision millingof the end plates. In a preferred aspect, the burr template end face maybe angled with respect to the distraction window such that a burr may becontrolled to remove an angled surface of the end plate.

The present invention also includes a guide assembly for a bladedcutting instrument. The guiding assembly includes a slot adapted toreceive a blade and a guide channel for maintaining alignment of theblade in the slot. In a preferred aspect, the slot and guide channel aredisposed at an oblique angle permitting removal of a portion of avertebra. In still a further preferred aspect, the guiding assembly isadapted for guiding instruments into the spine from an oblique-anteriorapproach. In this further aspect, the guiding assembly includesangulation to account for the oblique angle approach to the spine andcompounding angulation to create the desired angle of the removedvertebral bone.

The present invention further contemplates a distractor for anoblique-anterior approach to the spine. In one preferred aspect, thedistractor includes a substantially straight leading portion and anangled leading portion. Still further, it is preferable for maintainingor establishing angulation between adjacent vertebrae that thedistractor have a head with a tapered portion oriented at an angle withrespect to the longitudinal axis of the distractor. In one preferredembodiment, the offset is approximately 30 degrees.

The invention further contemplates a distraction window configured foroblique engagement to the spine. In one preferred aspect, the boneengaging surfaces are arcuate and including a leading portion extendingmore distally than a trailing portion. In still a more preferredembodiment, the distraction window includes distraction flangesconfigured to maintain angulation between adjacent vertebrae. Theflanges preferably include a taper oriented at an offset with respect tothe longitudinal axis.

In still a further aspect of the invention, a chisel adapted for obliquecutting of the vertebra is provided. The chisel comprises a firststraight cutting edge and a second angled cutting edge. In a preferredaspect, the chisel further includes a third angled cutting edge shorterthan the first angle portion.

The present invention further contemplates a method of disc space andendplate preparation from an anterior approach to the spine as furtherdescribed and disclosed herein. Still more preferably, the anteriorapproach is from an oblique angle to the spine. In this aspect, themethod includes gaining access to an oblique portion of the spine,inserting a distractor from an oblique angle and engaging a distractionwindow from the oblique angle. A cutting guide may then be engaged withthe distraction window and the endplates may then be prepared from theoblique angle. In a preferred aspect, the endplates are prepared toinclude a taper between adjacent vertebrae.

These and other objects of the present invention will become apparentfrom a review of the accompanying drawings and the detailed descriptionof the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a distractor disposed between twoadjacent vertebral bodies from a direct anterior approach to the spine.

FIGS. 2 a and 2 b are a side and top view, respectively, of thedistractor of FIG. 1.

FIG. 3 is a perspective view of the drawing of FIG. 1 further includinga guiding assembly according to another aspect of the present invention.

FIG. 4 is a perspective view of the guide assembly of FIG. 3 positionedadjacent the disc space and the distractor removed.

FIG. 5 a is a perspective view of a distraction window according to oneaspect of the present invention.

FIG. 5 b is a top view of the distraction window of FIG. 5 a.

FIG. 5 c is a side view of the distraction window of FIG. 5 a.

FIG. 5 d is a cross-sectional side view taken along line 5 d—5 d of FIG.5 b.

FIG. 6 a is an exploded perspective view of an alternative embodiment ofa distraction window according to another aspect of the presentinvention.

FIG. 6 b is a side view of the distraction window of FIG. 6 a.

FIG. 6 c is a front view of the distraction window of FIG. 6 a.

FIG. 6 d is a top view of the distraction window of FIG. 6 a.

FIG. 7 a is a side view of a retaining shaft for use with the guidesleeve of the present invention.

FIG. 7 b is an end view of the guide shaft of FIG. 7 a.

FIG. 8 is a perspective view of a distraction window according to thepresent invention disposed between adjacent vertebrae.

FIG. 9 is an exploded perspective view of rotary cutting guide assemblyaccording to another aspect of the present invention.

FIG. 10 is a perspective view of the rotary cutting guide of FIG. 9 inan assembled configuration.

FIG. 11 a is a side view of the rotary cutting guide of FIG. 9.

FIG. 11 b is a rear view of the rotary cutting guide of FIG. 11 a.

FIG. 11 c is a front view of the rotary cutting guide of FIG. 11 a.

FIG. 11 d is a bottom view of the rotary cutting guide of FIG. 11 a.

FIG. 11 e is a top view of the rotary cutting guide of FIG. 11 a.

FIG. 12 a is a partial cross-sectional top view of a guide tubeaccording to another aspect of the present invention.

FIG. 12 b is an end view of the guide tube of FIG. 12 a.

FIG. 13 a is a perspective view of a guide tube linkage according to thepresent invention.

FIG. 13 b is an end view of the guide tube linkage of FIG. 13 a.

FIG. 13 c is a side view of the guide tube linkage of FIG. 13 a.

FIG. 14 is a perspective view of an alternative guide tube assemblyaccording to the present invention.

FIG. 15 a is a perspective view of a guide block according to thepresent invention.

FIG. 15 b is a side view of the guide block of FIG. 15 a.

FIG. 15 c is a rear view of the guide block of FIG. 15 a.

FIG. 15 d is a front view of the guide block of FIG. 15 a.

FIG. 15 e is a cross-sectional side view taken along line 15 e—15 e ofFIG. 15 d.

FIG. 16 is a perspective view of a cutting blade guide assemblyaccording to another aspect of the present invention.

FIG. 17 a is a side view of the guide block of FIG. 16.

FIG. 17 b is a rear end view of the guide block of FIG. 16.

FIG. 18 a is a top plan view of a chisel blade configured for use withthe guide block of FIG. 16.

FIG. 18 b is a side view of the chisel blade of FIG. 18 a.

FIG. 19 a is a perspective view of an implant insertion assemblydisposed adjacent a vertebral body.

FIG. 19 b is an enlarged perspective view of the implant insertionassembly according to FIG. 19 a.

FIG. 20 a is a top plan view of an implant according to the presentinvention disposed adjacent a prepared vertebral body.

FIG. 20 b is a perspective view of the implant and vertebral body ofFIG. 20 a.

FIG. 21 is a perspective view of a distractor disposed between twoadjacent vertebral bodies from an oblique anterior approach to thespine.

FIGS. 22 a through 22 c are bottom, side and top views, respectively, ofthe distractor of FIG. 21.

FIGS. 23 a through 23 d are top, rear end, front end and partialcross-section side view, respectively, of the distractor head of FIG.21.

FIG. 23 e is perspective side view taken along line 23 e—23 e of FIG. 23a.

FIG. 24 is a perspective view of a distractor and guide tube assemblyaccording to a preferred aspect of the present invention.

FIG. 25 is a perspective view of the guide tube assembly of FIG. 24disposed between adjacent vertebrae.

FIG. 26 is a perspective view of the distraction window of FIG. 25.

FIG. 27 a through 27 e are side, top, perspective, rear end, and frontend views, respectively, of the distraction window of FIG. 26.

FIG. 28 is a perspective view of the distraction window and a guideblock according to another aspect of the present invention.

FIG. 29 is a perspective view of a guide block assembly and chisel.

FIG. 30 a is a side view the guide block of FIG. 28.

FIG. 30 b is a front end view of the guide block of FIG. 30 a.

FIG. 30 c is a rear end view taken along line 30 c—30 c of FIG. 30 a.

FIG. 31 a is a side view an alternative guide block.

FIG. 31 b is a front end view of the guide block of FIG. 31 a.

FIG. 31 c is a rear end view taken along line 31 c—31 c of FIG. 31 a.

FIG. 32 is a top view of a chisel blade according to the presentinvention.

FIG. 33 is a side view of the chisel blade of FIG. 32

FIG. 34 a is a perspective view of a guide tube and implant inserteraccording to the present invention.

FIG. 34 b is an enlarged top view of the a portion of FIG. 34.

FIG. 35 is a perspective view of a vertebra and implant.

FIG. 36 is an alternative perspective view of the implant and vertebraof FIG. 35.

FIG. 37 is another perspective view of the implant and vertebra of FIG.35.

FIG. 38 is a top view of a depth gauge in combination with a distractionwindow according to another aspect of the present invention.

FIGS. 39 a and b are a top view and side view, respectively, of thedepth gauge of FIG. 38.

FIG. 40 is a top view of a depth gauge in combination with a distractionwindow according to another aspect of the present invention.

FIGS. 41 a and 41 b are a top view and side view, respectively, of thedepth gauge of FIG. 40.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein, beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

The present invention relates to instruments and methods for gainingaccess to a disc space between adjacent vertebral bodies, distractingthe disc space to a desired height, preparing the disc space to receivean implant to maintain disc space height and angulation, and a methodfor inserting an implant into the prepared disc space. Morespecifically, while methods and instruments disclosed in the presentapplication may have application in other areas of the spine or thebody, it is specifically contemplated that the present instruments andmethod may be utilized in an anterior approach to the spine forimplantation of various implant devices. Still more specifically, thepresent invention contemplates a direct anterior approach to the spinefor implant placement as well as an anterior-oblique approach to thespine for disc space preparation and implant placement. It will beunderstood that an anterior-oblique approach to the spine may bedesirable in certain areas of the spine where a direct anterior approachis difficult or impossible because of patient anatomy. The term implantsin the present application is used in a broader sense to encompass bothload bearing implants constructed of man-made materials, as well as loadbearing implants formed of naturally occurring materials. Further,implants contemplated to be used with the present invention may includethose intended to promote fusion between adjacent vertebra as well asartificial disc replacements. Implant inserters and specific implantsare disclosed in U.S. Provisional Application entitled “INSTRUMENTS ANDIMPLANTS FOR MULTI-DIRECTIONAL INSERTION OF A VERTEBRAL SPACER,” filedFeb. 22, 2000, which is incorporated herein by reference in itsentirety.

Referring now to FIG. 1, there is shown a partial spinal columnconsisting of vertebra V1 and vertebra V2 separated by a disc space D.It will be understood that access to disc space D is obtained by knownsurgical techniques and will not be described further herein. With thedisc space D exposed, distractor 8 is positioned adjacent disc space Dfrom a direct anterior approach. With respect to the view of FIG. 1, theX axis represents the anterior to posterior direction, the Y axisextends laterally, while the X axis extends in the superior to inferiordirection. As shown in FIG. 1, distractor 8 is inserted substantiallyparallel to the X axis. The position of distractor 8 in terms ofanatomical position is substantially parallel to the sagittal and axialplanes. Distractor 8 includes an elongated shaft 10 having a proximalend with a tool adapter 12 to receive a tool handle (not shown) and adistal end having a distraction head 14.

Referring to FIGS. 2 a and 2 b, distraction head 14 further comprisesopposing tapered leading surfaces 20 and 24 adapted to engage and spreadthe vertebrae as the surfaces are advanced into the disc space D. Aguiding fin 18 is centrally disposed on distraction head 14. Guiding fin18 has a height greater than tapered leading surfaces 20 and 24 as wellas the overall height of distraction plug 16 such that guiding fin 18may extend into the vertebral bone and guide the distractor into thedesired position. The use of a guiding fin on a distractor is furtherdisclosed in U.S. patent application Ser. No. 09/418,741, which isincorporated herein in its entirety. Distraction plug 16 may take manyknown configurations including having tapered surfaces adapted toestablish and maintain desired angulation between adjacent vertebrae.Further, distractor head 14 includes an arcuate bone engaging surface 26and an opposing bone engaging surface on the bottom side, each adaptedto engage the anterior portions of the respective upper and lowervertebral bodies.

In use, distractor 8 of FIG. 1 is disposed adjacent disc space D. Forceis applied to shaft 10 to urge distractor head 14 into disc space D. Asdistractor head 14 advances into disc space D tapered leading surfaces20 and 24 engage end plates E1 and E2, respectively urging vertebra V1and V2 apart and maintaining the distraction height by disposing therest of distraction plug 16 within disc space D.

Referring now to FIGS. 3 through 5 d, there is shown a guide tubeassembly adapted to be received over distractor 8 of FIG. 1. Guide tubeassembly includes a distraction window 30 and a selectively coupledguide tube 32 with a removable guide cap 34. Referring more specificallyto FIGS. 5 a–5 d, distraction window 30 includes a working channel 45configured to slidingly receive centering block 22 of distractor 8.Extending distally from distraction window 30 is distraction holder 36and opposing distraction holder 40. The distraction holders are adaptedand configured to extend into the disc space D and engage end plates E1and E2 to maintain the distraction obtained with distractor 8. Further,each of the distraction holders includes an external taper on itsleading surface adapted to urge tissue to the exterior of the window andaway from working channel 45. Distraction holders also include boneengaging surfaces, such as ridges 47 and 49 shown in FIG. 5 c withrespect to distraction holder 40, to inhibit dislodgment once positionedin the disc space. Additionally, distraction window includes arcuatebone engaging surfaces 42 and 44 adapted to engage the arcuate anteriorportions of V1 and V2, respectively. Preferably, a spike 38 extends frombone engaging surface 42. Spike 38 is intended to penetrate vertebra VIto provide additional stability to distraction window 30. Workingchannel 45 is interrupted by annular shoulder 46 marking the transitionfrom the proximal portion 51 of larger dimension to the smallerdimensions of the distal working area 53 of distraction window 30. Thedistal working area 53 includes slightly tapering side walls.Distraction window 30 also includes a recess 48 on its upper surface.

Guide tube 32 includes a substantially rectangular working channel 62adapted and configured to correspond with the proximal dimensions ofworking channel 45 of distraction window 30. While a rectangular workingchannel is disclosed in the present application, it will be understoodthat it is contemplated that working channels having substantiallycircular, oval, FIG. 8 or any other cross-sectional configurations maybe utilized for disc space preparation and implant insertion. Guide tube32 includes a front flange adapted to engage the proximal portion ofdistraction window 30. Guide tube 32 also includes retaining assembly 54that may be utilized to selectively couple guide tube 32 to distractionwindow 30. Referring to FIG. 4, retaining assembly 54 includes an outershaft 64 coupled to guide tube 32. An inner shaft 60 extending along thelength of outer tube 64. A finger lever 56 coupled to the proximal endof inner shaft 60 and a retaining foot 58 disposed on the distal portionof inner shaft 60. Inner shaft 60 is shown in more detail in FIGS. 7 aand 7 b. The position of inner shaft 60 with respect to outer shaft 64is maintained by pin 68 extending into annular groove 70.

An alternative version of a distraction window assembly is shown inFIGS. 6 a–6 d. Distraction window assembly 80 includes selectivelycoupled distraction holders 82 and 84. It will be understood thatdistraction holders of various heights and angulations may be utilizedwith distraction window body 81 thereby providing a reduced number ofwindow assemblies that must maintained in a sterilized condition for useby the operating staff. Distraction holders 82 and 84 may be quicklyinserted or changed to meet the various demands of a particular surgerysimply by removing retaining clip 86.

Distraction holder 82 includes a pair of opposing dove tail projections98 and 100. A corresponding channel 92 is formed in distraction windowbody 81. Channel 92 includes a pair of opposed dove tail recesses 94 and96 adapted to matingly receive dove tail projections 98 and 100,respectively. Retaining groove 104 extends on the upper portion ofdistraction window body 81 as well as along the sides of the distractionwindow assembly. Retaining groove 104 extends into channel 92 and in asimilar fashion with respect to the retention of distraction holder 84.The intersection of channel 92 and 93 with retaining groove 104 createsopenings 102 and 106, respectively. Groove 83 is formed on distractionholder 82 such that when disposed within channel 92 groove 83 issubstantially aligned with slot 102. Distraction holder 84 is configuredin substantially similar manner to mate with channel 93 and includes asimilar retaining groove to align with slot 106. With distraction holder82 disposed within channel 92 with the proximal portion abuttinglyreceived against end wall 108, retaining ring 86 may be positionedwithin groove 104 thereby extending a portion of retaining ring 86 intogroove 83 to hold distraction holder within the distraction window body81.

Distraction window body 81 further includes an upper and lowerprojection 90 and 80, respectively. Projections 90 and 80 furtherinclude bores 91 and 89, respectively, configured to receive pins thatmay extend into the vertebra to further retain the distraction windowassembly in relation to the vertebral bodies. Further, pins extendingthrough bores 91 and 88 tend to maintain arcuate vertebral bone engagingsurfaces 114 and 116 in intimate contact with the anterior portions ofthe vertebral bodies. Thus, distraction window assembly 80 defines aworking channel 112 for access to the disc space and portions of theupper and lower vertebral bodies.

Distraction window 30 may be coupled to guide tube 32 by initiallybringing guide tube 32 into a butting engagement with distraction window30 such that flange 50 surrounds at least a portion of distractionwindow 30. Lever 56 may then be rotated to cause retaining foot 58 torotate into recess 48 on distraction window 30. With retaining foot 68extending into recess 48, distraction window 30 and guide tube 32 arethereby removably coupled to one another. Referring now to FIG. 3, theguide tube and distraction window assembly may then be advanced overdistractor 8 with the distraction window assembly 30 guided into placeby engagement with centering block 22 of distractor 8. Cap 34 may bepositioned over flange 52 and force applied to the cap, such as byhammering, to advance distraction holders 36 and 40 into the disc spaceand pin 38 into the bone of the vertebra. Once the guide tube anddistraction window assembly have been properly positioned, cap 34 may beremoved and a handle attached to distractor 8 at coupling 12. Once ahandle is attached to coupling 12, distractor 8 may then be forciblyremoved from the disc space leaving the guide tube and window assemblypositioned as shown in FIG. 4. Lever 56 of retaining assembly 54 maythen be rotated in an upward direction thereby causing retaining foot 58to rotate out of recess 48 on distraction window 30. With retaining foot58 positioned out of recess 48, guide tube 32 may be disengaged fromdistraction window 30. Thus, as shown in FIG. 8, distraction window 30retains it's position in the disc space and adjacent the anteriorportions of vertebra V1 and V2 with distractor holders 36 and 42engaging end plates E1 and E2 to maintain the disc space height andangulation established by distractor 8. As shown in FIG. 8, portion 72of vertebra V1 and portion 74 of vertebra V2 are accessible throughdistraction window 30.

Referring now to FIGS. 9–15 e, there is shown a rotating tool guideadapted for utilization with a distraction window 30 according to thepresent invention. Guide assembly 120 includes a guide housing 125 shownin greater detail in FIGS. 15 a–15 e. Guide housing 125 includes aninsert end 124 configured to be received within proximal portion 51 ofdistraction window 30. It will be understood that distal end 127 ofguide housing 125 abuttingly engages wall 46 in distraction window 30.Further, the walls of insertion end 124 are configured to be asubstantially close fit with the walls defining proximal portion 51 ofdistraction window 30. Further, surface 123 of guide housing 125 isconfigured to engage the proximal most portion of distraction window 30.Thus, guide housing 125 is adapted to have insertion portion 124matingly received within the proximal portion 51 of window assembly 30.Insertion end 124 is a substantially close fit with the dimensions ofproximal portion 51 such that there is little movement of the guidehousing with respect to the distraction window in directions other thanproximally toward the user.

Guide housing 125 further includes cutting window 128. In a preferredembodiment, particularly useful for fashioning vertebral end plates toestablish and/or maintain angulation between adjacent vertebra, uppersurface 176 and lower surface 177 of cutting window 128 are disposed atan angle A1 with respect to the longitudinal axis 179. Flange 129 isdisposed within cutting window 128 and may act as a bearing surface forelements of the guiding assembly. As further described herein, theangulation of cutting window 128 with respect to the longitudinal axis179 permits end plate cutting and preparation at an angle desirable tomaintain and/or establish an angular relationship between adjacentvertebrae. Further, guide face 126 and flange 129 are set at acorresponding angle A2 with respect to the longitudinal axis. It will beunderstood that the angulation of guide face 126 provides a side wall142 that tapers between the upper surface 144 to a greater thickness atbottom surface 146. Thus, guide face 126 and flange 129 provide areference plane for the attachment of other guiding elements such thatthey may be maintained in the proper angular relationship with the angleof cutting window 128. Internally threaded bore 178 is defined inhousing 125 and is disposed at an angle substantially equal to a angleA1. In a preferred embodiment, threaded bore 174 is disposed equidistantbetween sidewalls 142 and 143 such that it is substantially centeredwith respect to the lateral dimensions of guide block 125.

Guide assembly 120 further includes a guide tube 130 shown in greaterdetail in FIGS. 12 a and 12 b. Guide tube 130 includes a through channel131 having a proximal end with an internal chamfer 152 configured toguide and align a tool shaft as it is inserted. Further, internalchannel 131 includes an annular flange 154 dividing areas of larger andsmall diameter of working channel 131. In a preferred embodiment, guidetube 130 is interconnected by linkage 132 to a linkage post 156.Preferably, the interconnection between guide tube 130, linkage 132, andguide post 156 is substantially rigid and does not permit pivotalmovement of one member with respect to the other. Guide post 156 furtherincludes an axial bore 158 defining an internal thread. Anothercomponent of guide assembly 120 includes guide post 134 having an axialbore 164 extending there through. Preferably, guide post 134 is rigidlyinterconnected with linkage tube 160. Linkage tube 160 includes an axialbore 162 extending there through.

Guide assembly 120 is assembled by placing linkage post 156 within bore162 of linkage tube 160. Assembly screw 150 is then inserted withexternal threads threadedly engaging the internally threaded bore 158.Head 170 is sized to be larger than bore 162 such that assembly screw150 retains linkage. Assembly screw 150 may be tightened by atool-engaging slot if desired. The interconnection between linkage post156 and linkage tube 160 permits rotation of linkage tube about linkagepost. Distal portion 133 of guide tube 130 is then disposed withinwindow 128 and guide post 134 is aligned with threaded opening 174 suchthat internal bore 164 is in substantial alignment with threaded bore174. An elongated assembly screw with a shaft sufficient to extendthrough bore 164 is utilized to attach guide post 134 to housing 125.The connection between housing 125 and guide post 134 permits pivotingof guide post 134 about the shaft of assembly screw 148. Further, asshown in FIG. 11 a, guide tube 130 and guide post 134 are disposed at anangle A1 with respect to the longitudinal axis 179 of housing 125. Thus,guide tube is in substantial alignment with cutting window 128 and willbe maintained in substantial alignment throughout the cutting process.

Referring to FIG. 14, an alternative embodiment of a guiding assemblyaccording to the present invention is shown. Guiding assembly 185includes a housing 125, guide tube 186 and linkage 187. A portion ofguide tube 186 is received within linkage 187 as described above withrespect to the embodiment of FIG. 9. Post 188 extends the length oflinkage 187 and fixedly engages housing 125. Post 188 may be engaged tohousing 125 by, but without limitation, threads, pinning, welding,adhesive, or any other suitable mechanism. Post 188 further includes agroove at its proximal end. Preferably, a snap ring 189 may be insertedinto the groove to retain the linkage on post 188. Preferably, snap ring189 is easily removed to permit disassembly. While a snap ring has beendisclosed other removable connection mechanisms may be used. It iscontemplated that the linkage and guide tube may be used with multiplehousings having various angulations and heights.

Referring now to FIGS. 9 and 10, guide assembly 120 may be inserted intodistraction window 130 with insertion end 124 securely received withindistal portion 51. In a preferred embodiment a burr may be received withthe cutting bit 136 extending into channel 131 and substantially beyondchannel 131 with the ability to engage and cut exposed vertebral bone orother tissues. Shaft 138 is substantially received within channel 131with large portion 140 abuttingly engaging annular flange 154 to limitthe axial extent cutting instrument 122 may extend within guide 120.Shaft 138 is sized to be a snug fit within channel 131 to provideprecise guiding of the cutting bit 136. In a preferred aspect, cuttinginstrument 122 will further include a coupler 139 for attachment to apower source to drive cutting bit 136. Only a particular cuttinginstrument has been shown for use with the guide of the presentinvention. However, it is contemplated that other alternative cuttinginstruments, including hand operated instruments, may be utilized incombination with the guide assembly of the present invention, it beingunderstood that the guide assembly 120 provides controlled cutting ofangular surfaces with the angle of cut being substantially maintainedover a large lateral distance. Further, guide tube 130 and theaccompanying linkage not only maintain the vertical angulation of thecutting instrument but also maintain the cutting instrument in asubstantially fixed side-to-side angulation thereby limiting thepotential for accidental penetration into tissues along the lateralextent of the disc space. More specifically, guide tube 130 maintainsthe orientation of cutting bit 136 substantially perpendicular bothhorizontally and vertically with respect to flange 129 and guide face126.

Referring now to FIG. 16, there is another perspective view ofdistraction window 30 in combination with a cutting blade guide 210 anda cutting instrument 250. As previously discussed with respect to guideassembly 120, blade guide 210 includes an insertion end 224 configuredfor engagement with proximal portion of distraction window 30. Bladeguide 210 includes a blade channel 214 defined by opposed surfaces 217and 215. In a preferred aspect, opposed surfaces 215 and 217 aresubstantially parallel and extend at an angle A4 with respect to thelongitudinal axis 219. In one embodiment, angle A4 is approximately 4degrees. However, it is contemplated that angle A4 may vary between 0degrees and 30 degrees depending on patient anatomy and the amount ofbone to be removed. Blade guide assembly 210 further includes a guidechannel 216 defined by opposed side walls 218 and 220 and lower guidesurface 222. These surfaces also extend at an angle A4 with respect toaxis 219. Guide assembly 210 also includes an internally threaded bore230 and an enlarged external flange 226 having a surface 228 adapted toabuttingly engage the proximal edge of distraction window 30. FIGS. 17 aand 17 b further disclose a tooling ball 225 utilized during themanufacturing process as a reference point for manufacturing the variousangled surfaces of the guide assembly. It will be understood thattooling ball 225 is preferably removed after manufacture.

Referring now to FIGS. 18 a and 18 b, cutting instrument 250 includes ablade 252, a stop 254 disposed on the proximal portion of blade 252, ashaft 256 interconnected with a handle 258. Blade 252 includes a cuttingblade having a first leading blade 260, a first lateral cutting blade261, and a second lateral cutting blade 262. Cutting blades 261 and 262are preferably set with an angle A5 with respect to the longitudinalaxis 263. In a preferred embodiment, A5 is approximately 30 degrees.Blade 252 further includes guiding rib 264 extending substantially alongthe longitudinal axis of the blade and having a height substantiallytaller than the blade thickness. It will be understood that guiding ribis configured to slidingly engage guide channel 216 formed in guidehousing 210. Blade 252 further includes a stop 254 having a leading face268 disposed at an angle A6 with respect to the longitudinal axis of theblade. Preferably angle A6 is between 80 and 100 degrees in a morepreferred aspect is 94 degrees. Leading edge 268 is adapted toabuttingly engage the face of housing 210 to prevent further advancementof blade 252. The trailing edges of blade 252 include tapered surfaces266 and 267 set at an angle A7, which preferably is 60 degrees. Blade252 is attached to shaft 256.

Referring to FIG. 16, it will be understood that as cutting instrument250 enters guide 210 the leading elements of blade 252 engage theexposed vertebral bone (see FIG. 8) and continue at the designated anglethereby removing a portion of the vertebral end plate at the desiredangular relation. Viewing window 212 of housing 210 permits the user toremove the cutting debris and view the end plate to determine ifpreparation has been completed.

Referring to FIGS. 38 through 39 b, there is shown a depth gaugeaccording to the present invention. Depth gauge 700 includes a shaft 702interconnected with a depth blade 707. Depth blade 707 has an elongatedportion 704, wide body portion having side walls 705 and 706, andproximal shoulders 708 and 710. Referring to FIG. 38, depth gauge 700may be inserted into window 30 and into the disc space to visuallyevaluate the intended depth of cut into the vertebral endplates. Sidewalls 705 and 706 maintain alignment in window 30 while shoulders 708and 710 are configured to engage the proximal end of window 30 to limitfurther advancement. With shoulders 708 and 710 engaged with window 30,elongated portion 704 approximates the distance for a given cutterdepth. It will be understood that a variety of depth gauges may beprovided to approximate various depths of bone removal.

Guided end plate preparation by both rotary cutting means and cuttingblades has been disclosed in the foregoing description. It will beunderstood that the thickness of vertebral bone removed, the angle ofthe cut and the side-to-side movement (if any) is precisely controlledby the design of the guides. Guides allowing varying incremental boneremoval are contemplated to provide the ability to adjust endplatepreparation depths without removal of the distraction window.Furthermore, controlled end plate preparation of the upper vertebralbone has been disclosed, it being understood that the guides may berotated 180 degrees and inserted into the distraction window forsubstantially similar preparation of the lower end plate.

After a disc space has been prepared including removal of the desiredamount of end plate bone at the desired angle, an implant may beinserted through distraction window 30. Referring now to FIGS. 19 a and19 b, guide tube 32 is preferably reattached to distraction window 30 aspreviously described. An insertion device 290 configured for insertionthrough the guide tube and distraction window may then be utilized.Insertion device 290 represents an example of such an insertion device.Implant inserter 290 includes an outer shaft 294, an inner shaft 296having a threaded distal end and a thumb wheel 292 attached on aproximal end. The inner shaft is free to rotate within outer shaft 294.The distal end of the insertion device includes implant engagingsurfaces 297, 298, and 299. It being understood that preferably surfaces297, 298, and 299 have an angular relationship substantially matchingthe surface of the implant. Further descriptions of other suitableimplant inserters and implants are provided in Provisional Applicationentitled “INSTRUMENTS AND IMPLANTS FOR MULTI-DIRECTIONAL INSERTION OF AVERTEBRAL SPACER,” filed on Feb. 22, 2000, and is hereby incorporated byreference in its entirety.

In use, the implant includes an internal bore and thumb wheel 292 isrotated such that externally threaded internal shaft 296 engages aninternal bore on the implant firmly positioning the implant against theimplant engaging surfaces 297, 298, and 299. The implant and inserteradvance through the guide tube 32 and through distraction window 30until the implant is positioned in channel C2 prepared an end plate E2of vertebra V2 and a corresponding channel of the end plate of the upperopposed vertebra. Implant 300 is retained in position betweendistraction holding members 36 and 40 in the prepared disc space. In apreferred aspect, implant 300 is entirely disposed within the boundariesof vertebra V2 and is oriented to maintain proper angulation betweenadjacent vertebral bodies. The relationship of implant 300 with respectto vertebra V2 is shown more clearly in FIGS. 20 a and 20 b.

Referring to drawing FIGS. 21–39 c, there are disclosed instruments andtechniques for approaching the spine from an anterior-oblique direction.With respect to patient anatomy, the spine is approached in substantialalignment with the axial plane and at an oblique angle with respect tothe sagittal plane. It is believed that precision guided techniques andinstrumentation for an oblique-anterior approach to the spine have notbeen previously available.

Referring specifically to FIG. 21, a portion of the spine including twoadjacent vertebrae V3 and V4 are shown with disc space D2 disposedbetween the adjacent vertebrae. The vertebrae are shown in a perspectiveview from a substantially anterior perspective. As the XYZ coordinatesystem illustrates, the X coordinate comes substantially out of thepaper, the Y coordinate extends from left to right, and the Z coordinateextends from top to bottom of the drawing FIG. 21. A distractor 408 isshown disposed in disc space D2 and is oriented in the disc space alonglongitudinal axis 411. Reference line 413 is drawn substantiallyparallel to X-axis and forms an angle A10 with longitudinal axis 411.While it is contemplated that an oblique approach to the spine may bemade at a variety of non-orthogonal angles, in a preferred aspect of theinvention angle A10 is approximately 30 degrees.

Distractor 408 includes elongated shaft 410, a tool engaging end 412adapted to engage a driving or retrieval tool and a distraction head 414disposed on the distal end of shaft 410. Distractor 414 includes acentering block 422 and inclined surfaces on the proximal portiontending to align a guide sleeve with centering block 422. With respectto drawing FIGS. 23 a–23 e a tool ball 452 is shown. The tool ball 452is utilized during the manufacturing process to insure proper alignmentfor the various machining operations. It is contemplated that thetooling ball will be removed from the finished product after themanufacturing process is substantially complete.

Referring now to FIGS. 23 a–e, the centering block 422 incline surfacesinclude upper surface 458 and opposed lower surface 460 combined withopposing side surfaces 462 and 466. Distraction head 414 furtherincludes a leading edge 440 and an angled leading edge 442. As shown inFIG. 23 a, angled leading edge 442 is disposed at an angle A12 withrespect to leading edge 440. In a preferred embodiment, angle A12 isapproximately 30 degrees corresponding to the oblique angle of approachto the anterior spine. Adjacent leading edge 440, distraction head 414has a top tapered surface 434 and a bottom tapered surface 436.Similarly, adjacent angled leading edge 442 there is a top tapered andangled surface 438 and a bottom angled tapered surface 436. Angledsurfaces 438 and 436 are formed in a plane extending substantially 30degrees with respect to similar surfaces 434 and 432. Top taperedsurfaces 434 and 438 lead to upper distraction surface 434 while lowertapered surfaces 432 and 436 lead to lower distraction surface 436.Upper distraction surface 444 terminates into upper bone engagingsurface 428. In a similar manner lower distraction surface 446terminates in bone engaging surface 426. Bone engaging surface 428, andin a similar fashion lower bone engaging surface 426, are defined by aconcave arcuate surface based on an off center radius of curvature.Specifically, upper bone engaging surface 428 has a leading edge 468extending more distally than trailing edge 470. In a preferred aspect,leading edge extends substantially 6 mm more distally than trailing edge470.

As shown in FIG. 23 a, a slot 448 is formed through the leading portionof distraction head 414. Slot 448 is offset from side wall 456 bydistance D10 and is offset from opposing side wall 454 by distance D11.In a preferred aspect, distance D10 is greater than distance D11resulting in slot 448 being substantially off center with respect to thecenterline of distraction head 414. A guiding fin 430 having a heightgreater than corresponding portions of distraction head 414 may bedisposed in slot 448 and held in position by pins 450 extending therethrough. Guiding fin 430, shown in FIGS. 22 a–c, is adapted to engagethe vertebral bone and cut a guiding channel through the bone tomaintain the proper direction of distraction head 414 during theinsertion process. Still further, a bore 466 is formed in the rear ofdistraction head 414 and is utilized for interconnection with shaft 410.

It is contemplated that instruments according to the present inventionmay be utilized from an anterior-oblique approach for distraction on thevertebra having a non-parallel angular relationship. In this instance,establishing and/or maintaining the appropriate angular relationshipbetween adjacent vertebra must be considered when approaching the discspace from an oblique angle. Thus, in one aspect of the preferredembodiment, upper distraction 444 and lower distraction surface 446 aredisposed at an angle approximating the desired angular relationship ofthe vertebral disc space. While such angulation may vary from 0 degreesto 20 degrees throughout the spine, particular angles of 4 degrees to 12degrees of angulation are often encountered in lumbar spinalapplications. The angular relationship of the upper distraction surface448 and lower distraction surface 446 is best shown in FIG. 23 e and isindicated by angle A14. In this embodiment, A14 is approximately 8degrees. FIG. 23 e is a side view of FIG. 23 a looking at an angle ofapproximately 30 degrees with respect to longitudinal axis 451. Thus,angulation A14 between the upper and lower distraction surfaces isoriented at approximately a 30 degree angle with respect to thelongitudinal axis of the device such that as the instrument is insertedinto the disc space from an oblique approach, the appropriate posteriorto anterior angulation of the vertebral end plates may be accomplished.

Referring now to FIG. 24, a guide tube 520 and distraction window 510coupled by a locking mechanism 522 may be slidingly advanced alongdistractor 408. The locking mechanism between guide tube 520 anddistraction window 510 is similar to that previously discussed withrespect to the embodiment shown in FIG. 3 and will not be furtherdescribed herein. As shown in FIG. 26, guide tube 520 may be removed togain access to the disc space D2 and end plate E4 at portion 516.

Referring to FIG. 26, distraction window 510 defines an interior workingchannel 512 separated into a distal portion and a proximal portion 544by internal flange 514. Distraction window 510 includes distractionprojections 518 and 517 disposed on opposite sides of the device.Distraction projections 518 and 517 when adapted for use with lordoticangulation include a taper corresponding to the angle of distractor 408oriented at a 30 degree angle with respect to the longitudinal axis 513.Further, distraction window 510 includes upper bone engaging surface 536and lower bone engaging surface 538, each having a concave engagementsurface with an offset radius of curvature. The bone engaging surfaces536 and 538 are adapted to engage the anterior portions of the upper andlower vertebrae respectively. As shown in FIG. 27 b, upper bone engagingsurface includes a leading 542 and a trailing portion 540. Leadingportion 542 extends approximately 6mm more distally than trailingportion 540 in a preferred embodiment. The extent that leading portionextends beyond the trailing portion depends on the oblique angleselected for access to the spine, the width of the window and the sizeof the vertebra to be engaged. Preferably, upper bone engaging surface436 includes a spike 424 for projecting into the upper vertebral body.As previously described, distraction window 510 includes a recess 526for engaging a locking mechanism of guide tube 520.

Referring now to FIG. 28, there is shown the distraction window 510disposed between vertebra V3 and vertebra V4. A guide block 550 havingan insertion end 552 configured for engagement with proximal end 544 isalso disclosed therein. The details of guide block are more fully shownin FIGS. 30 a–c. Guide block 550 defines a blade guide 554 having anupper surface 668 and a lower surface 666. Specifically, the blade guideincludes a guide channel 570 defined by a lower surface 588 and twoopposed side walls 592 and 594. Guide block 550 further includes avisualization and working channel 556. Blade guide 554 proceeds at anangle from the front 557 to the back 559 at an angle of A13. Referringspecifically to FIG. 30 a, reference line 572 represents a linesubstantially parallel to the longitudinal axis of the guide lock andreference line 574 extends in a line substantially parallel to bladeguide 554. Reference lines 572 and 574 are disposed at an angle of A13.In a preferred aspect, A13 may be approximately 3.5 degrees, howeverother angulations are contemplated as maybe desired depending on theanatomy of the spinal segment being treated.

Blade guide 554 is also oriented at an angle extending from side 556 to553. Referring now to FIG. 30 c, a front view of FIG. 30 a viewed at anangle of approximately 3.5 degrees. Reference line 562 is substantiallyparallel to the top surface 569 of block 550. Reference line 564 issubstantially parallel to upper and lower surfaces 668 and 666, of bladeguide 554. Reference lines 562 and 564 are disposed at an angle A17. Inone preferred aspect, A17 is substantially 2 degrees. In anotherpreferred aspect, reference angle A17 is substantially 4 degrees. Otherangles of side-to-side angulation are contemplated and will depend onthe particular anatomy of the spine to be addressed. Thus, blade guideopening 554 is set at a compound angle including a front-to-backangulation and a side-to-side angulation. Guide block 550 furtherincludes an internally threaded bore 578 adapted to receive a portion ofa handle to hold the guide block. As with previous describedembodiments, a tooling ball 560 is provided to provide a reference pointfor creating the various compound angle surfaces. The reference ball 560is intended to be removed once the manufacturing process issubstantially complete.

Referring to FIGS. 31 a–31 c, guide block 595 is provided for preparingthe bottom end plate. Guide block 595 is substantially a mirror image ofguide block 550 and includes a blade guide opening 597 and guide channel598 having angulation resulting in substantially mirror image guideblade slot when compared to guide block 550. The angle of guide bladefrom front to back is represented by A16 and is approximately 3.5degrees. The angulation from side-to-side is represented by angle A15and is approximately 2 degrees in a preferred embodiment shown indrawing FIG. 31 c.

Referring now to FIG. 33, a cutting blade 586 is shown for utilizationwith the upper guide block shown in FIG. 30 a–c. Guide blade 586includes a guiding rib 610 extending above the surface of the guideblade. Guide rib 610 is adapted to be received within guide and channel670. Blade 586 further includes a leading cutting edge 616, a largeangled cutting edge 618, and a smaller cutting edge 620. Angled cuttingedge 618 and 620 extend at a substantially 30 degree angle with respectto cutting edge 616. Large angled cutting edge 618 is approximately 3times longer than cutting edge 620. A lower cutting blade or chisel (notshown) having substantially the mirror image of chisel 586 is providedfor use in lower guide block 595 to prepare the lower vertebral endplatefor receiving an implant. The lower cutting blade includes a guiding ribthat is offset from the center line such that it will not fit in theupper guide block. Similarly, the lower guide block has a guidingchannel that is offset from center line such that it may receive thelower cutting blade guide rib but not the upper cutting blade guide rib.

Referring to FIGS. 40 through 41 b, there is shown a further depth gaugesuitable for use in the oblique approach to the spine. Depth gauge 800includes a shaft 802 interconnected with a blade 804. Blade 804 includesleading edges 806, 808, and 810 approximating the geometry of thecutting edges of the chisels previously described. Blade 804 has a widthdefined by side walls 812 and 814. Shoulders 816 and 818 are formed onthe proximal end of blade 804. Referring now to FIG. 40, blade 804 maybe inserted into window 510 to evaluate the area of cut that will beperformed with a particular dimension of chisel. Blade 804 may be guidedlaterally be engagement of side walls 812 and 814 with portions ofwindow 510 and longitudinally by engagement of shoulders 816 and 818with the proximal end of window 510. In this position, the surgeon mayevaluate visually, through x-ray, or any other means, the area of boneintended to be removed. It will be understood that various length blades804 may be provided to approximate various length chisels.

An implant inserter such as shown in FIGS. 34 a and b is provided toadvance an implant to the disc space. Inserter 650 is substantially aspreviously described with respect to the inserter of FIG. 19 a. Implantinserter 650 includes an outer shaft 654 with an inner shaft disposedtherein and having a thumb wheel 652 on the proximal for transmittingrotation force to drive the opposing threaded end of the inner shaft(not shown) into a corresponding opening in implant 670. Implantinserter 650 has modified implant engaging surfaces 656, 658 and 660adapted to correspond to the surfaces of implant 670 disposed atapproximately a 30 degree angle to the approach for grasping theimplant. Implant 670 is sized and configured for advancement throughguide sleeve 520 and distraction window 510 and placement in the discspace from an oblique anterior approach to the spine.

Referring to FIGS. 35 through 37, the final placement of implant 670 inchannel or cut C4 in vertebra V4 is shown. Posterior surface 672 is insubstantial alignment with posterior portion 676 of vertebra V4.Similarly, anterior surface 674 is in substantial alignment withanterior portion 678 of vertebra V4. Further, the taper between theupper and lower bone engaging surfaces of implant 670, shown by angleA20, extends from the posterior to anterior portion with increasingheight. Thus, implant 670 may maintain angulation between adjacentvertebra.

The present invention contemplates a method of guided disc space andendplate preparation from an oblique approach to the spine. The methodis initiated by obtaining access to an oblique anterior portion of thespine. This includes well known approaches to the anterior of the spineas well as any required vessel retraction by previously knownprocedures. Once an oblique portion on the anterior spine adjacent theaffected disc space is exposed, all or part of the disc material may beremoved. A distractor 408 is then advanced into the disc space from anoblique angle to the spine. For applications where it is desirable toachieve or maintain angulation between adjacent vertebral endplates,distractor 408 may include a desired taper, extending at an anglecorresponding to the oblique angle of approach to the spine, toestablish the proper angulation. Referring to FIG. 24, after distractionan interconnected distraction window 510 and guide tube 520 are advancedover distractor 408. Distraction window 510 includes distraction flangeshave tapering heights, when viewed at the oblique angle of approach tothe spine, to maintain the angulation previously established by thedistractor. The distraction flanges are advanced into the spine and thebone engaging surfaces of the distraction window are brought into closeproximity to the anterior portions of the upper and lower vertebralbodies. With the distraction window properly position in and adjacentthe disc space, distractor 408 is removed. Guide tube 520 may also beuncoupled from distraction window 510 and removed. The locking mechanismpermits uncoupling from the proximal end of guide tube 520 thus limitingthe need for additional vessel retraction adjacent distraction window510 to permit a surgeon to access a locking mechanism.

The distraction window 510 provides a surgeon with clear access to thedisc space and vertebral endplates. As shown in FIG. 40, a depth gaugemay be inserted through window 510 to evaluate the depth and area ofbony endplate to be removed. Further, distraction window 510 provides aplatform for guided preparation of the vertebral body endplates.Referring to FIG. 28, a guide block 550 is slidably received in proximalportion 544 of the distraction window. Insertion portion 552 isconfigured for a relatively close fit with proximal portion 544, therebylimiting relative movement between the distraction window and guideblock. If additional connection between the distraction window and guideblock is desired, a locking mechanism may be provided to releasably lockthe guide block to the distraction window.

Referring to FIG. 29, a chisel 580 or other non-rotating cuttinginstrument is inserted into blade guide 554 of the guide block. In apreferred embodiment intended for preparing endplates with a desiredangulation, the blade guide includes a compound angular relation to thedistraction window. Specifically, blade guide includes an obliqueside-to-side angle as well as an oblique front-to-back angle. In afurther preferred aspect, the cutting blade includes a guiding ridge 610adapted to be received within guiding channel 670 thereby providingadditional control over the blade advancement.

The cutting blade is advanced through the upper blade guide and acorresponding portion of vertebral endplate is removed. The debris fromthe cutting procedure may be removed with the guide block still in placeor the guide block may be disengaged from the distraction window and thedebris removed. Once the debris is removed, the endplate may be visuallyinspected. If the user desires the removal of additional endplate bone,a guide block permitting an incrementally greater amount of boneremoval, typically in 1 mm increments, may be substituted for guideblock 550 and the cutting blade reinserted. Once the upper endplate issatisfactorily prepared, a lower guide block 595 may be inserted intodistraction window 510. A cutting blade cooperable with the lower guideblock is inserted into blade guide 597 and utilized to similarly preparethe lower endplate.

Once the upper and lower vertebral endplates have been properly preparedwith cuts or channels adapted to receive an implant, the guide blocksare removed from the distraction window. Preferably, guide tube 520 isreconnected to distraction window 510. An implant is interconnected withan implant inserter and the implant is positioned through the guide tubeand distraction window into the disc space. Despite the fact that theimplant has been inserted from an oblique angle to the spine, the guideddisc space preparation permits placement of tapered implant in theproper orientation in the disc space. The final implant placement shownin FIGS. 35 through 37 is comparable to the implant placement shown inFIGS. 20 a and b accomplished by a direct anterior approach to thespine. Thus, the present method of implant placement provides a newguided approach to the spine that may be particularly useful wherepatient anatomy makes direct anterior or lateral approaches to the spinedifficult and/or dangerous to patient health.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

1. A medical instrument for preparation of a disc space between adjacentvertebrae of a patient, comprising: a burr assembly adapted to matinglyengage a window assembly that is coupled to between the adjacentvertebrae, said burr assembly including a guide housing having a cuttingslot defined therein, and a guide assembly pivotally linked to saidguide housing, said guide assembly being adapted to guide a cuttingpiece in said cutting slot while maintaining alignment of said cuttingpiece.
 2. The instrument of claim 1, wherein said guide assembly isconstructed and arranged to guide said cutting piece at an oblique anglewith respect to a sagittal plane of the patient.
 3. The instrument ofclaim 1, wherein said burr assembly includes an incremental adjustmentmechanism adapted to incrementally adjust cutting depth of said cuttingpiece.
 4. The instrument of claim 1, further comprising said cuttingpiece removably coupled to said guide assembly.
 5. The instrument ofclaim 4, wherein said guide assembly angles said cutting piece to millan angled surface on an end plate of one of the vertebrae.
 6. Theinstrument of claim 4, wherein said cutting piece includes a shaft and acutting bit provided at one end portion of said shaft, said shaft havinga large portion to limit extension of said cutting piece into thevertebrae.
 7. The instrument of claim 1, wherein said guide assemblyincludes a guide tube having a through channel adapted to receive saidcutting piece, said cutting slot having a flange portion in which aportion of said guide tube is received, said guide tube furtherincluding a linkage and a linkage post extending from said linkage, saidguide assembly further including a linkage tube pivotally coupled tosaid guide housing and said linkage post.
 8. The instrument of claim 7,further comprising a snap ring attaching said linkage tube to said guidepost.
 9. The instrument of claim 1, wherein said guide assemblymaintains angular alignment of said cutting piece during lateralmovement of said cutting piece.
 10. The instrument of claim 1, furthercomprising said window assembly matingly engaged to said burr assembly,wherein said window assembly is adapted to attach to the adjacentvertebrae from an oblique approach with respect to a sagital plane ofthe patient.
 11. The instrument of claim 1, wherein: said guide housingincludes a distal insert end; and said window assembly includes aproximal portion having a wall extending about a proximal opening, andsaid distal insert end fits in said wall in substantially close fittherewith through said proximal opening.
 12. The instrument of claim 1,wherein said guide housing extends proximally and distally along alongitudinal axis and said cutting slot opens through said guide housingproximally and distally at an angle relative to said longitudinal axisto orient said cutting piece to cut said endplate at said angle.
 13. Theinstrument of claim 1, wherein: said guide housing extends proximallyand distally along a longitudinal axis; and said guide housing includesa proximal guide face extending about said cutting slot, said guide faceforming an angle with said longitudinal axis, wherein said angle orientssaid cutting piece extending proximally and distally through saidcutting slot at an angle relative to said longitudinal axis.
 14. Theinstrument of claim 13, wherein said guide face includes an internallythreaded bore extending therethrough into said guide housing, said guideassembly being linked to said guide housing in said bore.
 15. Theinstrument of claim 1, wherein: said guide assembly includes a postengaged at a distal end to said guide housing and extending proximallyfrom said guide housing; and a linkage rotatably received about saidpost, said linkage including a guide tube extending therealong, saidguide tube including a distal end position in said cutting slot, saidguide tube being movable along said cutting slot across said guidehousing by rotating said linkage about said post.
 16. A medicalinstrument for preparation of a disc space between adjacent vertebrae ofa patient, comprising: a burr assembly adapted to matingly engage awindow assembly that is coupled to between the adjacent vertebrae, saidburr assembly including: a guide housing adapted to fit within saidwindow assembly, said guide assembly having a cutting slot definedtherein opening proximally and distally in said guide housing; and aguide assembly including a post engaged at a distal end to said guidehousing and extending proximally from said guide housing, said guideassembly including a linkage rotatably received about said post, saidlinkage including a guide tube extending therealong, said guide tubeincluding a distal end position in said cutting slot and being movablealong said cutting slot across said guide housing by rotating saidlinkage about said post.
 17. The instrument of claim 16, wherein saidguide housing includes an internal bore extending therein, said postbeing engaged to said guide housing in said internal bore.
 18. Theinstrument of claim 17, further comprising a snap ring attaching saidlinkage to said post.
 19. The instrument of claim 16, wherein: saidguide housing includes a distal insert end; and said window assemblyincludes a proximal portion having a wall extending about a proximalopening, and said distal insert end fits in said wall in substantiallyclose fit therewith through said proximal opening.
 20. The instrument ofclaim 16, wherein said guide housing extends proximally and distallyalong a longitudinal axis and said cutting slot opens through saidhousing proximally and distally at an angle relative to saidlongitudinal axis to permit a cutting piece in said guide tube extendingthrough said cutting slot to cut said endplate at said angle.
 21. Theinstrument of claim 16, wherein: said guide housing extends proximallyand distally along a longitudinal axis; and said guide housing includesa proximal guide face extending about said cutting slot, said guide faceforming an angle with said longitudinal axis, wherein said angle orientsa cutting piece in said guide tube extending through said cutting slotat an angle relative to said longitudinal axis.
 22. A medical instrumentfor preparation of a disc space between adjacent vertebrae of a patient,comprising: a burr assembly adapted to matingly engage a window assemblythat is coupled to between the adjacent vertebrae, said burr assemblyincluding: a guide housing extending proximally and distally along alongitudinal axis, said guide housing having a cutting slot thereacrossand opening proximally and distally through said guide housing in adirection of said longitudinal axis, said cutting slot forming an anglerelative to said longitudinal axis in the proximal and distaldirections; and a guide assembly pivotally linked to said guide housing,said guide assembly being adapted to guide a cutting piece in saidcutting slot to cut an endplate of the adjacent vertebrae at said anglewhile maintaining alignment of said cutting piece at said angle.
 23. Theinstrument of claim 22, wherein said guide housing includes a proximalguide face extending about said cutting slot, said guide face forming asecond angle with said longitudinal axis, wherein said second angleorients said cutting piece in said cutting slot at said angle relativeto said longitudinal axis.
 24. The instrument of claim 23, wherein: saidguide assembly includes a post engaged at a distal end to said guidehousing and extending proximally from said guide housing; and a linkagerotatably received about said post, said linkage including a guide tubeextending therealong, said guide tube including a distal end positionedin said cutting slot, said guide tube being movable along said cuttingslot across said guide housing by rotating said linkage about said post.